Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The disclosed method relates to manufacturing a heat exchanger which
causes no brazing defects, and a heat exchanger manufactured by the
method. The method relates to manufacturing a heat exchanger having an
aluminum alloy tube defining a cooling-medium flowing passage and a
copper alloy tube defining a water flowing passage, wherein a heat
exchange is carried out between a cooling medium flowing through the
cooling-medium flowing passage and water flowing through the water
flowing passage. The aluminum alloy tube and the copper alloy tube are
brazed to each other at a temperature of less than 548° C.

Claims:

1. A method of manufacturing a heat exchanger having an aluminum alloy
tube defining a cooling-medium flowing passage and a copper alloy tube
defining a water flowing passage, wherein a heat exchange is carried out
between a cooling medium flowing through the cooling-medium flowing
passage and water flowing through the water flowing passage, and wherein
said aluminum alloy tube and said copper alloy tube are brazed to each
other at a temperature of less than 548.degree. C.

2. The manufacturing method as set forth in claim 1, wherein the brazing
is carried out by using a brazing material which is composed of
Al--Cu--Si based alloy or an Al--Cu--Si--Zn based alloy.

3. The manufacturing method as set forth in claim 2, wherein said
Al--Cu--Si based alloy or said Al--Cu--Si--Zn based alloy contains at
least one of Cu in an amount of up to 27 mass % and Si in an amount of up
to 5.5 mass %.

4. The manufacturing method as set forth in claim 3, wherein a ratio of
liquid phase mass created in the brazing material produced from said
Al--Cu--Si based alloy or said Al--Cu--Si--Zn based alloy to a total mass
of the brazing material is at least 60% at the temperature of 548.degree.
C.

5. A heat exchanger manufactured by the method as set forth in claim 1.

6. A heat exchanger manufactured by the method as set forth in claim 2.

7. A heat exchanger manufactured by the method as set forth in claim 3.

8. A heat exchanger manufactured by the method as set forth in claim 4.

Description:

BACKGROUND

[0001] The disclosed method relates to a method of manufacturing a heat
exchanger and so forth, used in a heat pump type hot-water supply system,
in which a cooling medium is may function as a heat source, and to a heat
exchanger manufactured by such a manufacturing method.

BACKGROUND ART

[0002] In a heat pump type hot-water supply system in which a CO2
cooling medium subjected to a high temperature and a high pressure is
employed as a heat source, heat exchange is carried out between the
cooling medium and the water to thereby heat the water, and the hot-water
supply system has widely prevailed in recent years. In a heat exchanger
used in this known hot-water supply system, in general, a copper alloy
tube of heat conductivity and high corrosion resistance is utilized as
one of the composition elements. However, for the purpose of improvement
in transportability and cost reduction, it has been proposed that an
aluminum alloy tube featuring high heat conductivity, lightness and low
cost is utilized for a cooling medium passage.

[0003] In a conventional heat exchanger in which copper alloy tubes are
utilized for a cooling medium flow-passage and a water flow-passage,
respectively, since a joining is made between the copper alloy tubes, a
variety of joining methods such as a furnace brazing method, a soldering
method and so forth has been put into practice. Nevertheless, it is known
that a joining between an aluminum alloy and a copper alloy is very
difficult due to the fact that there are many problems such as a
difference in temperature of approximately 400° C. between
respective melting points of the aluminum alloy and the copper alloy;
that a firm oxide film exists on a surface of the aluminum alloy; and so
on.

[0004] JP 2002-107069 A discloses a heat exchanger in which an aluminum
alloy cooling-medium tube and a copper alloy water tube are utilized. In
this heat exchanger, the aluminum alloy cooling-medium tube and the
copper alloy water tube are mechanically joined to each other. Also, in a
heat exchanger disclosed in JP 2010-255869 A, an aluminum alloy
cooling-medium tube and a copper alloy water tube are joined to each
other by using a brazing material.

[0005] JP 2000-117484 A discloses a method of brazing an aluminum alloy
and a copper alloy to each other by using a brazing material. In this
method, it is used for such a brazing material, an Al--Si--Cu-based alloy
which features a total contents of an Si element and/or a Cu element
falling within a range from 5 mass % to 15 mass %, or an Al-based brazing
material which contains Al, Si of 10 mass %, Cu of 4 mass %, Zn of 10
mass %, and a brazing process is carried out at a temperature of
approximately 600° C. Also, JP 2006-341304 A discloses a method of
brazing an aluminum alloy and a copper alloy to each other by using a
Zn--Al-based brazing material.

[0006] In the heat exchanger of JP 2002-107069 A, the aluminum alloy
cooling-medium tube and the copper alloy water tube are mechanically
joined to each other. In this case, due to the fact that the respective
rates of thermal expansion in both the alloys are different from each
other, when a temperature difference between the flowing water and the
cooling medium becomes larger, a thermal stress is generated at the
joined region of both the alloys. Thus, a deformation occurs in the
joined region of both alloys, so that a uniform join state (i.e., a close
contact state) cannot be maintained in the joined region of both the
alloys, resulting in deterioration in heat exchanging effectiveness.

[0007] In the heat exchanger of JP 2010-255869 A, it is not concretely
taught what components the brazing material are composed of, and thus an
erosion may occur depending on a type of the used brazing material. In
this case, as shown in FIG. 1, the erosion is defined as a phenomenon in
which a member to be joined is eroded by a melted brazing material. In
FIG. 1, reference "2" indicates the aluminum alloy cooling-medium tube;
reference "3" indicates a copper alloy water tube; reference "4"
indicates a brazing material; and a portion 1 encircled by a solid
ellipse represents an erosion-occurring region.

[0008] In a case where a brazing process is carried out by using the
brazing method disclosed in JP 2000-117484 A, due to the fact that a
brazing temperature is more than a eutectic temperature (548° C.)
of both the aluminum alloy and the copper alloy, a eutectic-melting
occurs and there is a possibility that members to be joined to each other
would be subjected to a deformation. In this case, the eutectic-melting
is defined as a phenomenon in which a join junction between the aluminum
alloy material and the copper alloy material is locally melted, and FIG.
2 is a view showing that the eutectic-melting progresses so that the
joined members may be subjected to a large deformation. In FIG. 2,
reference "5" indicates an aluminum alloy plate; reference "6" indicates
a copper alloy tube; and reference "7" indicates a brazing material.
After the brazing process, configurations of both the aluminum alloy
plate and the copper alloy tube were subjected to a remarkable
deformation due to the melting.

[0009] In the method of brazing the aluminum alloy and the copper alloy to
each other by using the Zn--Al-based brazing material, as disclosed in JP
2006-341304 A, since the Zn--Al-based brazing material is insufficient in
corrosion resistance, it is difficult to apply the brazing method to a
heat exchanger which is possibly exposed to a severe corrosive
environment.

SUMMARY

[0010] The invention relates to a method of manufacturing a heat exchanger
having an aluminum alloy tube defining a cooling-medium flowing passage
and a copper alloy tube defining a water flowing passage, wherein a heat
exchange is carried out between a cooling medium flowing through the
cooling-medium flowing passage and water flowing through the water
flowing passage, and wherein said aluminum alloy tube and said copper
alloy tube are brazed to each other at a temperature of less than
548° C. The brazing is carried out by using a brazing material
which is composed of Al--Cu--Si based alloy or an Al--Cu--Si--Zn based
alloy. The Al--Cu--Si based alloy or the Al--Cu--Si--Zn based alloy
contain at least one of Cu in an amount of up to 27 mass % and Si in an
amount of up to 5.5 mass %. A ratio of liquid phase mass created in the
brazing material produced from the Al--Cu--Si based alloy or the
Al--Cu--Si--Zn based alloy-to a total mass of the brazing material is at
least 60% at the temperature of 548° C. The invention also relates
to a heat exchanger made by the method.

Problems to be Resolved

[0011] The disclosed method may be applied such as to a heat exchanger
used in a heat pump type hot-water supply system, in which a cooling
medium is employed as a heat source. In particular since an aluminum
alloy tube having cooling-medium flowing passages and a copper alloy tube
having water flowing passages are brazed to each other at a temperature
which is lower than a eutectic temperature (548° C.) of both the
aluminum alloy and the copper alloy, it is possible to provide not only a
method of manufacturing a heat exchanger but also a heat exchanger
manufactured by such a method which causes little or no brazing defects
such as a eutectic melting, an erosion and so forth.

[0012] In a first aspect, the present invention-relates to a method of
manufacturing a heat exchanger having an aluminum alloy tube that has a
cooling-medium flow passage and a copper alloy tube that has a water flow
passage, wherein heat exchange is carried out between a cooling medium
flowing through the cooling-medium flow passage and water flowing through
the water flow passage, where the aluminum alloy tube and the copper
alloy tube are brazed to each other at a temperature of less than
548° C. The aluminum alloy may include a pure aluminum material,
and the copper alloy may include a pure copper material.

[0013] In a second aspect, the present invention relates to a
manufacturing method, wherein the brazing is carried out by using a
brazing material which is composed of an Al--Cu--Si based alloy or an
Al--Cu--Si--Zn based alloy.

[0014] In a third aspect, the present invention relates to a manufacturing
method, wherein the brazing material which is composed of either the
Al--Cu--Si based alloy or the Al--Cu--Si--Zn based alloy contains at
least one of: Cu in an amount of up to 27 mass % and Si in an amount of
up to 5.5 mass %.

[0015] In a fourth aspect, the present invention relates to a
manufacturing method, wherein a liquid phase ratio, which is defined as
the ratio of liquid phase mass created in the brazing material that is
either the Al--Cu--Si based alloy or the Al--Cu--Si--Zn based alloy, to
the total mass of the brazing material, is at least 60% at 548° C.

[0016] In a fifth aspect, the present invention relates to a heat
exchanger manufactured by any one of the methods as set forth above.

Effects of the Invention

[0017] In a heat exchanger manufacturing method according to the present
invention, and a heat exchanger manufactured by the method, since an
aluminum alloy tube having cooling-medium flow passages and a copper
alloy tube having water flow passages can be brazed to each other without
any brazing defects, it is possible to provide a heat exchanger featuring
a superior heat exchanging efficiency.

BRIEF EXPLANATIONS OF DRAWINGS

[0018]FIG. 1 (Prior art) is a microscope photograph showing an erosion
which occurred when an aluminum alloy material and a copper alloy
material were brazed to each other.

[0019]FIG. 2 (Prior art) is a photograph showing a eutectic-melting which
occurred when an aluminum alloy material and a copper alloy material were
brazed to each other.

EMBODIMENT FOR CARRYING OUT THE INVENTION

[0020] The present invention is explained in detail below.

[0021] (1) Brazing Temperature:

[0022] The brazing temperature, at which an aluminum alloy cooling-medium
tube and a copper alloy water tube are brazed to each other, is less than
548° C. This is because a eutectic-melting occurs in the aluminum
alloy and the copper alloy at the temperature which is equal to or more
than 548° C., so that a member(s) to be joined (i.e., the aluminum
alloy cooling-medium tube and/or the copper alloy water tube) is
subjected to a deformation and/or a decline in strength. In order that a
brazing material can be sufficiently melted, a lower limit of the brazing
temperature is preferably equal to or more than 510° C. Thus,
preferably, the brazing temperature is within a range from at least
510° C. to less than 548° C.

[0023] (2) Composition of Brazing Material:

[0024] In the present invention, for the brazing material, it is possible
to use either Al--Cu--Si based alloy or Al--Cu--Si--Zn based alloy. When
either the Al--Cu--Si based alloy or the Al--Cu--Si--Zn based alloy is
used, a liquidus curve temperature can be lowered to less than the
eutectic temperature (548° C.) of both the aluminum alloy and the
copper alloy, and thus the brazing process can be carried out at a
temperature below the eutectic temperature. Accordingly, it is possible
to carry out the brazing process, in which the deformation and the
strength decline of the member(s) to be joined can be suppressed, without
occurrence of eutectic-melting in both the aluminum alloy and the copper
alloy.

[0025] It is preferable that the Al--Cu--Si based alloy or the
Al--Cu--Si--Zn based alloy which is used in the present invention
contains at least one of: Cu in an amount of up to 27 mass % (referred to
as "%" hereinafter) and Si of in an amount of up to 5.5%. Cu and Si are
added to each of the alloys enhance liquidity of the brazing material.
The addition of Cu and Si serves to lower the liquidus curve temperature
of the brazing material. When the content of Cu is more than 27%, and/or
when the content of Si is more than 5.5%, the enhancement of the
liquidity of the brazing material is too much so that an erosion may
occur in the brazing material. When erosion occurs in the brazing
material, a strength, corrosion resistance and brazing ability decline,
resulting in deterioration in performance of a heat exchanger. Although
an alloy containing either Cu or Si of 0% is included in neither the
Al--Cu--Si based alloy nor the Al--Cu--Si--Zn based alloy, such an alloy
may be used for the brazing material.

[0026] In the brazing material that includes Al--Cu--Si--Zn based alloy,
the addition of Zn lowers the liquidus curve temperature of the brazing
material. Also, the addition of Zn serves to give a lower potential to
the brazing material, and thus it is possible to regulate a potential of
the brazing material so that an erosion resistance in a heat exchanger
can be improved. Nevertheless, when the content of Zn is too much, an
erosion resistance of the brazing material conspicuously declines, so
that the content of Zn is preferably present in an amount of up to 20%.

[0027] Note, concerning the inevitable impurities which are necessarily
contained in a raw material for producing the brazing material, when Fe
impurity is 0.3% or less, when the remaining impurities are 0.05% or
less, and when a total percentage of the impurities is 0.15% or less, it
is possible to obtain a heat exchanger according to the present invention
without impairing its characteristic.

[0028] When the brazing material produced from either the Al--Cu--Si based
alloy or the Al--Cu--Si--Zn based alloy has a liquid phase ratio of less
than 60% at 548° C., and when a brazing process is carried out at
less than 548° C., an amount of liquid phase which is necessary
for the brazing process is small so that there may be a case where a
brazing junction cannot sufficiently form. Thus, preferably, the brazing
material should have a liquid phase ratio of at least 60% at 548°
C. Herein, the liquid phase ratio is defined as the ratio of a liquid
phase mass, which is created in the brazing material produced from either
the Al--Cu--Si based alloy or the Al--Cu--Si--Zn based alloy, to the
total mass of the brazing material concerned.

[0029] It is very difficult to measure a real liquid-phase ratio during a
heating process. Thus, the liquid-phase ratio is calculated by using an
equilibrium calculation. The liquid-phase ratio is calculated by using
thermodynamic equilibrium calculation program software such as
"Thermo-Calc Software made by AB Corporation" or the like, on the basis
of a composition of the alloy brazing material and a heating temperature
thereof.

[0030] (3) Form or Shape of Brazing Material:

[0031] In general, it is possible to provide the brazing material in a
powder form, a rod-like form, a foil form or a cladded form (i.e., a
cladded material) in which a brazing material is previously cladded on a
member to be joined. When a brazing process is carried out by using an
aluminum alloy brazing material according to the present invention, it is
preferable to use the brazing material in either the powder form or the
foil form.

[0032] a) Powder-Form Brazing Material:

[0033] Powder form brazing material preferably has an average grain
diameter falling within a range from 10 μm to 150 μm. When the
average grain diameter is less than 10 μm, it is impossible to
completely remove oxide films from the powder brazing material during a
brazing process, and thus there is a case where a defect easily may occur
at a brazed junction. Also, when the average grain diameter is more than
150 μm, there may be a case where it is difficult to coat a surface of
an aluminum alloy tube with the powder brazing material in a suitable
amount, and thus the brazing material is ununiform in an amount over a
brazed region, so that a defect such as an erosion may be caused.

[0034] b) Foil-Form Brazing Material:

[0035] Preferably, a foil-form brazing material has a thickness falling
within a range from 0.1 mm to 0.2 mm. When the foil-form brazing material
has a thickness of less than 0.1 mm, there may be a case where the
foil-form brazing material having such a thickness is not suitable for a
mass production because a production thereof is too costly. Also, when
the foil-form brazing material has a thickness of more than 0.2 mm, an
absolute amount of the brazing material becomes large, so that a defect
such as an erosion may be caused.

[0036] (4) Flux:

[0037] a) Kind of Flux:

[0038] In general, when a brazing process is carried out, a flux is used
to remove oxide films which cover surfaces of both a brazing material and
a member to be joined. As such a flux, it is possible to utilize a
fluoride-based flux, a chloride-based flux or a mixture composed of the
fluoride-based flux and the chloride-based flux, which are used when a
brazing process for a usual aluminum alloy is carried out. For a
representative of the fluoride-based flux, there are KAlF4,
K2AlF5, K2AlF5.H2O, K3AlF6, AlF3,
KZnF3, K2SiF6, Cs3AlF6, CsAlF4.2H2O,
Cs2AlF5.H2O and so forth, and one of these fluxes may be
solely used, or a mixture composed of more than one of these fluxes may
be used. Also, for a representative of the chloride-based flux, there are
NaCl, KCl, LiCl, ZnCL2 and so forth, and one of these fluxes may be
solely used, or a mixture composed of more than one of these fluxes may
be used.

[0039] Due to the fact that removal of an oxide film must be carried out
before a brazing material is melted, the melting point of a flux that is
selected lower than that of the brazing material. It is preferable to use
a flux featuring a low melting point, such as the fluoride-based flux
including CsF, and the chloride-based flux including ZnCl2. Note, in
either the fluoride-based flux or the chloride-based flux, it is
effective to set the melting point to be at least 400° C.,
preferably, at least 450° C.

[0040] b) Coating of Flux:

[0041] In general, a flux is prepared as a slurry-like suspension in which
a flux component is suspended in a dispersion medium composed of a
volatile liquid such as an alcohol, a pure water or the like, a binder
and so forth, and a foil-form brazing material or a member to be joined
is coated with the flux.

[0042] When the powder-form brazing material is used, it is preferable
that the member to be joined is coated with a slurry-like suspension in
which the flux component is suspended together with the powder-form
brazing material in the aforesaid dispersion medium, so that the coat of
both the powder-form brazing material and the flux can be uniformly
applied to the member to be joined. Although a mixing ratio of the
powder-form brazing material and the flux may be changed in accordance
with a composition and a configuration of the member to be joined as well
as another member to be joined to the former member to be joined, it is
preferable to set the mixing ratio as a ratio of 10-150 weight parts of
the flux to 100 weight parts of the powder-form brazing material.

[0043] When the member to be joined is coated with either the slurry in
which the flux component is suspended or the slurry in which both the
flux component and the powder-form brazing material are suspended, a
coating method is not subjected to any limitation as long as the uniform
application of the coat of the slurry to the member to be joined is
ensured. It is possible to utilize not only a brush coating method or a
roll coating method but also an immersion coating method or a spray
coating method.

[0045] Although a method of pre-assembling the aluminum alloy
cooling-medium tube, the copper alloy water tube, and the brazing
material to be put therebetween is not subjected to limitation, when the
powder-form brazing material is used, a coat of the slurry containing
both the powder-form brazing material and the flux is applied to a member
to be joined, before or after the aluminum alloy cooling-medium tube and
the copper alloy water tube are pre-assembled into each other. When the
foil-form brazing material is used, a coat of the slurry containing the
flux component may be applied to a member to be joined, before or after
the aluminum alloy cooling-medium tube, the copper alloy water tube and
the foil-form brazing material are pre-assembled so that the foil-form
brazing material is put therebetween. Alternatively, after a coat of the
slurry containing the flux is applied to the foil-form brazing material
by using the roll coating method, or after the applied coat of the slurry
is dried, the aluminum alloy cooling-medium tube, the copper alloy water
tube and the foil-form brazing material are pre-assembled so that the
foil-form brazing material is put between the aluminum alloy
cooling-medium tube and the copper alloy water tube.

[0046] (6) Atmosphere in Brazing Process:

[0047] After the aluminum alloy cooling-medium tube, the copper alloy
water tube, and the brazing material to be put therebetween are combined
with each other, the combined regions therebetween are heated and brazed
to each other. Since the brazing material composed of the aluminum alloy
and the aluminum alloy cooling-medium tube are susceptible to
oxidization, it is preferable to carry out the heating/brazing process in
a non-oxidization atmosphere including an inert gas such as nitrogen gas,
an argon gas or the like or a reducing gas such as a hydrogen gas or the
like. Since the powder-form brazing material is further susceptible to
oxidization, preferably, a vacuum is created in the brazing environment,
and then the vacuum is filled with either inert gas or the reducing gas.

EXAMPLES

[0048] Next, the present invention is further explained with reference to
the Examples.

Examples 1 to 64 and Comparative Examples 65 to 69

[0049] (1) Preparation of Powder-Form Brazing Material:

[0050] Plural kinds of brazing materials in a powder form were used. In
order to obtain the plural kinds of powder-form brazing materials, plural
kinds of molten metals for aluminum alloys, which were composed of
respective compositions shown in TABLES 1, 2 and 3, the balances of Al,
and inevitable impurities, and which had a temperature of 750° C.,
were sprayed in an argon gas, and were rapidly cooled to thereby produce
plural kinds of aluminum alloy powders. These kinds of aluminum alloy
powders had respective average grain diameters shown in TABLES 1, 2 and
3.

[0052] For fluxes, CF-7, available from DAIICHI KIGENSO KAGAKU KOGYO CO.,
LTD, was used as a fluoride-based flux; FL-55, available from MORITA
CHEMICAL INDUSTRIES CO., LTD, was used as a chloride-based flux; and a
mixture of CF-7 and FL-55 was used as a mixture-based flux. CF-7 was
composed of Cs (55 mol %)-AlF3 (45 mol %), and the composition was
carried out so that the melting point of 410° C. could be
obtained. Also, FL-55 contained ZnCl2 of at least 40 mass %, and
NaCl--KCl--LiCl--LiF as another component, which were prepared so that
the melting point of 450° C. could be obtained. The mixture-based
flux was prepared so as to have CF-7 of 50 mass % and FL-55 of 50 mass %.
Each of the aforesaid three kinds of fluxes of 100 g and the powder-form
brazing material of 80 g were combined with each other, and was then
mixed with a commercially-available organic-substance-based binder of 100
g featuring a good volatility and pyrolytic property (more than 99.9% of
which could be vaporized) at a temperature of 410° C., resulting
in preparation of three kinds of slurries each of which contained the
flux and the powder-form brazing material.

[0053] (3) Pre-Assembly of Members to be Joined and Brazing Material:

[0054] In order to estimate a brazing property, multi-hole aluminum alloy
flat tubes (each of which had a thickness of 4 mm, a width of 20 mm and a
length of 150 mm, and was featured by seven hollows each having a width
of 2 mm, a height of 2 mm and a length of 150 mm) formed of 1050 aluminum
alloy and copper alloy flat tubes (each of which had a thickness of 1 mm,
a width of 20 mm and a length of 150 mm) were prepared.

[0055] One of the multi-hole aluminum alloy flat tubes and one of the
copper alloy flat tubes were combined with each other so that a lower
face (having the width of 20 mm and the length of 150 mm) of the
multi-hole aluminum alloy flat tube was in close contact with an upper
face (having the width of 20 mm and the length of 150 mm) of the copper
alloy flat tube, and a coat of any one of the aforesaid slurries was
intervened in a clearance between the multi-hole aluminum alloy flat tube
and the copper alloy flat tube, and was dried at a room temperature,
resulting in production of a brazing test sample assembly. Then, each of
the brazing test sample assemblies thus produced was placed in an
atmosphere oven, and a gas existed in an interior of the atmosphere oven
was replaced with any one of an argon gas, a nitrogen gas and a hydrogen
gas, as shown in TABLES 1 and 2. Thereafter, the brazing test sample
assembly concerned was heated in the atmosphere oven to 510° C.
over about 40 min., and then was maintained over a time period of 3 min.
at a corresponding brazing temperature falling within the range from
510° C. to 595° C. Then, the brazing test sample assembly
concerned was cooled to room temperature, resulting in completion of a
brazing process. In the cases where a chloride-based flux was used, each
of the brazing test sample assemblies was subjected to a water-washing
process after the brazing process to remove the residue of the
chloride-based flux from the brazing test sample assembly concerned.
Note, liquid phase ratios of the respective aluminum alloys at the
temperature of 548° C., which were calculated by using the
"Thermo-Calc Software", are shown in TABLES 1, 2 and 3.

[0056] Then, with respect to a join property, occurrence or non-occurrence
of a eutectic melting, and an erosion resistance, each of the brazing
test sample assemblies was estimated as a brazed test piece by using the
below-mentioned method methods. The Estimated results are shown in TABLES
4, 5 and 6.

[0058] Each of the brazed test pieces was longitudinally and vertically
cut off, and a light-microscopy cross-sectional observation was carried
out with respect to the cut section, to thereby estimate a join property
of the brazed test piece concerned, as a substitute for a property
representing a heat exchange ratio of a heat exchanger. In a brazed test
piece, when a ratio of an un-joined length to a full length of the join
junction was less than 5%, it was designated by symbol "{circle around
(∘)}". In a brazed test piece, when a ratio of an un-joined
length to a full length of the join junction was at least 5% but less
than 10%, it was designated by symbol "◯". In a brazed test
piece, when a ratio of an un-joined length to a full length of the join
junction was at least 10% but less than 20%, it was designated by symbol
"{circle around (∘)}◯". In a brazed test piece,
when a ratio of an un-joined length to a full length of the join junction
was at least 20% but less than 60%, it was designated by symbol
"Δ". In a brazed test piece, when a ratio of an un-joined length to
a full length of the join junction was at least 60% or when the join
junction could not be obtained, it was designated by symbol "×".
Note, in a brazed test piece, when an estimation could not be carried out
due to a remarkable deformation caused by a eutectic melting, it was
designated by symbol "--". The brazed test pieces, designated by any one
of the symbols "{circle around (∘)}", "◯",
"{circle around (∘)}◯" and "Δ", were judged
to be acceptable, and the brazed test pieces, which were designated by
the symbol "×" were judged to be unacceptable.

[0059] (5) Occurrence or Non-Occurrence of Eutectic Melting:

[0060] Each of the brazed test pieces was visually observed to determine
whether a eutectic melting occurred. In a brazed test piece, when no
eutectic melting occurred, it was designated by symbol "{circle around
(∘)}". In a brazed test piece, when a eutectic melting
occurred even at a part of the join junction, it was designated by symbol
"×". The brazed test pieces, designated by symbol "{circle around
(∘)}", were judged to be acceptable, and brazed test pieces,
which designated by the symbol "×", were judged to be unacceptable.

[0061] (6) Estimation of Erosion Resistance:

[0062] Each of the brazed test pieces was longitudinally and vertically
cut off, and a light-microscopy cross-sectional observation was carried
out with respect to the cut section. Then, an erosion ratio on the
brazing material, which was defined by a division, i.e., (the maximum
depth eroded by the brazing material from the boundary between the
brazing material and the member(s) to be joined, which was defined before
the brazing process)/(the thickness of the member(s) to be joined), was
calculated, to thereby estimate an erosion resistance. In a brazed test
piece, when the erosion ratio on the brazing material was less than 5%,
it was designated by symbol "◯". In a brazed test piece, when
the erosion ratio on the brazing material was at least 5% but less than
20%, it was designated by symbol "Δ". In a brazed test piece, when
the erosion was remarkable, and when the erosion ratio on the brazing
material exceeded 20%, it was designated by symbol "×". The brazed
test pieces, which were designated by either the symbol "◯"
or "Δ", were judged to be acceptable, and the brazed test pieces,
which were designated by the symbol "×", were judged to be
unacceptable.

[0063] (7) Comprehensive Judgment:

[0064] Based on the aforesaid test results, a comprehensive judgment was
performed on each of the brazed test pieces. In particular, when a brazed
text piece was designated by the symbol "{circle around (∘)}"
in each of the aforesaid tests, 7 points were given to it; when a brazed
test piece was designated by the symbol "◯" in each of the
aforesaid tests, 5 points were given to it; when a brazed test piece was
designated by the symbol "◯Δ" in each of the aforesaid
tests, 3 points were given to it; when a brazed test piece was designated
by the symbol "Δ" in each of the aforesaid tests, a zero point was
given to it; and when a brazed test piece was designated by either the
symbol "×" or "--" in each of the aforesaid tests, -5 points were
given to it. For the comprehensive judgment, when a brazed test piece
gained 17 points in total, it was designated by a symbol "{circle around
(∘)}"; when a brazed test piece gained at least 15 points and
less than 17 points in total, it was designated by a symbol
"◯Δ"; when a brazed test piece gained at least the zero
point and less than 13 points in total, it was designated by a symbol
"Δ"; when a brazed test piece gained less than the zero point in
total, it was designated by a symbol "×". In the comprehensive
judgment, the brazed test pieces, which were designated by any one of the
symbols "{circle around (∘)}", "◯"
"◯Δ" and "Δ", were judged to be acceptable, and
the brazed test pieces, which were designated by the symbol "×",
were judged to be unacceptable.

[0065] As shown in TABLES 4 and 5, in the comprehensive judgment, Examples
1 to 64 were acceptable.

[0066] On the other hand, as shown in TABLE 6, in the comprehensive
judgment, Comparative Examples 65 to 69 were unacceptable because of the
occurrence of the eutectic melting due to the fact that the brazing
temperature was too high.

Examples 70 to 117 and Comparative Examples 118 to 122

[0067] (1) Preparation of Foil-Form Brazing Material:

[0068] Plural kinds of brazing materials in a foil form were used. In
order to obtain the plural kinds of foil-form brazing materials, plural
kinds of molten metals for aluminum alloys, which were composed of
respective compositions shown in TABLES 7, 8 and 9, the balances of Al,
and inevitable impurities, were prepared, and an ingot was produced from
each of the plural kinds of molten metals by using a DC casting method.
Then, each of the ingots thus produced was processed into a foil-forma
brazing material by using ordinary methods. Thicknesses of the foil-form
brazing materials thus processed are shown in TABLES 1, 2 and 3.

[0070] For fluxes, CF-7, available from DAIICHI KIGENSO KAGAKU KOGYO CO.,
LTD, was used as a fluoride-based flux; FL-55, available from MORITA
CHEMICAL INDUSTRIES CO., LTD, was used as a chloride-based flux; and a
mixture of CF-7 and FL-55 was used as a mixture-based flux. CF-7 was
composed of Cs (55 mol %)-AlF3 (45 mol %), and the composition was
carried out so that the melting point of 410° C. could be
obtained. Also, FL-55 contained ZnCl2 of at least 40 mass %, and
NaCl--KCl--LiCl--LiF as another component, which were prepared so that
the melting point of 450° C. could be obtained. The mixture-based
flux was prepared so as to have CF-7 of 50 mass % and FL-55 of 50 mass %.
Each of the aforesaid three kinds of fluxes of 100 g was mixed with a
commercially-available organic-substance-based binder of 100 g featuring
a good volatility and pyrolytic property (more than 99.9% of which could
be vaporized) at a temperature of 410° C., resulting in
preparation of three kinds of slurries.

[0071] (3) Pre-Assembly of Members to be Joined and Brazing Material:

[0072] In order to estimate a brazing property, multi-hole aluminum alloy
flat tubes (each of which had a thickness of 4 mm, a width of 20 mm and a
length of 150 mm, and was featured by seven hollows each having a width
of 2 mm a height of 2 mm and a length of 150 mm) formed of 1050 aluminum
alloy, copper alloy flat tubes (each of which had a thickness of 1 mm, a
width of 20 mm and a length of 150 mm), and foil-form brazing materials
(each of which had a thickness of 0.1 mm, a width of 20 mm and length of
150 mm) were prepared.

[0073] One of the foil-form brazing material was immersed in any one of
the aforesaid three kinds of slurries containing the respective fluxes,
and was sandwiched between a lower face (having the width of 20 mm and
the length of 150 mm) of the multi-hole aluminum alloy flat tube and an
upper face (having the width of 20 mm and the length of 150 mm) of the
copper alloy flat tube, resulting in production of a brazing test sample
assembly. Then, each of the brazing test sample assemblies thus produced
was placed in an atmosphere oven, and a gas existed in an interior of the
atmosphere oven was replaced with any one of an argon gas, a nitrogen gas
and a hydrogen gas, as shown in TABLES 7, 8 and 9. Thereafter, the
brazing test sample assembly concerned was heated in the atmosphere oven
to 510° C. over a time period of about 40 min., and then was
maintained over a time period of 3 min. at a corresponding brazing
temperature falling within the range from 510° C. to 595°
C. Then, the brazing test sample assembly concerned was cooled to room
temperature, resulting in completion of a brazing process. In the cases
where a chloride-based flux was used, each of the brazing test sample
assemblies was subjected to a water-washing process after the brazing
process to thereby remove the residue of the chloride-based flux from the
brazing test sample assembly concerned. Note, liquid phase ratios of the
respective aluminum alloys at the temperature of 548° C., which
were calculated by using the "Thermo-Calc Software", are shown in TABLES
7, 8 and 9.

[0074] Then, with respect to a join property, occurrence or non-occurrence
of a eutectic melting, and an erosion resistance, each of the brazing
test sample assemblies was estimated as a brazed test piece in a similar
manner to the cases Examples 1 to 64 and Comparative Examples 65 to 69 as
mentioned above. The Estimated results are shown in TABLES 10, 11 and 12.

[0075] As shown in TABLES 10 and 11, in the comprehensive judgment,
Examples 70 to 117 were acceptable.

[0076] On the other hand, as shown in TABLE 12, in the comprehensive
judgment, Comparative Examples 118 to 122 were unacceptable because of
the occurrence of the eutectic melting due to the fact that the brazing
temperature was too high.

INDUSTRIAL APPLICABILITY

[0077] In a heat exchanger manufacturing method according to the present
invention, and a heat exchanger manufactured by the method, since an
aluminum alloy tube having cooling-medium flowing passages and a copper
alloy tube having water flowing passages can be well brazed to each other
without any brazing defects, it is possible to provide a heat exchanger
featuring a superior heat exchanging efficiency.